1. Field of the Invention
The present invention relates to a target substance detection method and a target substance detection kit for detecting a target substance in a specimen.
2. Description of the Related Art
A measuring method in which metal micro-particles are fixed on a base surface and a substance near the metal micro-particles is detected using localized surface plasmon resonance induced there is known. When light is incident onto metal micro-particles, such as gold and silver, a characteristic resonance spectrum appears by the localized surface plasmon resonance. It is known that its resonance wavelength is dependent on a dielectric constant of a medium near the metal micro-particles. As the dielectric constant becomes large, absorbance of a resonance peak becomes large and shifts to a long wavelength region. For example, Okamoto et al. have proposed a system using a gold colloid with a diameter of about 20 nm (Japanese patent No. 3452837 specification). This system is adapted to detect a refractive index of a certain medium by a distance which is about a diameter of a metal micro-particle fixed to the base, and consequently, it is possible to detect absorption and deposition of a substance (antigen in an antigen-antibody reaction) on a metal micro-particle surface.
In addition, Watanabe et al. have proposed a sensor technique which can measure an interaction concerning materials with high precision (Japanese Patent Application Laid-Open No. 2005-257667). Here, an example of labeling DNA with a dielectric crystal to be used for plasmon resonance is disclosed. Here, double stranded DNA constructed of DNA changed beforehand so as to become single stranded DNA when a target substance bonds together, and complementary DNA labeled with the dielectric crystal are immobilized on a detection surface where plasmon resonance occurs. When a target substance bonds with DNA on the detection surface, a distance between the dielectric and base changes and the target substance is detected using this change.
Nevertheless, detection methods which used the localized surface plasmon resonance and have been invented until now, have not been sufficient in detection sensitivity in an affinity assay such as an immunoassay using specificity of an antigen-antibody reaction or the like, and hence, further enhancement in the sensitivity has been desired.